Remote control system



Nov. 9, 1937. E. J. BLAKE 2,

REMOTE CONTROL SYSTEM Filed July 26, 1933 3 Sheets-Sheet l ELI J. BLAKE INVENTOR.

KM, I

A TTORNEY.

7 Nov. 9, 1937. E. J. BLAKE REMOTE (IJONTROL SYSTEM Filed July 26', 1935 3 Sheets-Sheet 2 INVENTOR 21 I BAA/(E.

ATTORNEY E. J. BLAKE 2,098,910

REMOTE CONTROL SYSTEM Filed July 26, 1935 5 Sheets-Sheet s Nov.'9,- 1937.

' 20 fic control are commonly comprised in a large connect the control station to the substations in Patented Nov. 9, 1937 l UNITED sm'rss rarest orrIcE REMOTE CONTROL SYSTEM Eli J. Blake, Haddonfield, N. J.; Elsie A. Blake, executrix of said Eli J. Blake, deceased Application July 26, 1933, Serial No. 682,229

38 Claims. (01. 2463) This invention relates to improvements in re switches at the control station and at the locamote control and supervision of scattered elections of controlled units. The present applicatrically operated units from a single control station discloses methods of accomplishing the tion, and more specifically to so-called centralsame ends which involve independently timed ized traflic control systems in which the control synchronous or time channel operation only in 5 of railway switches and signals distributed over a very rudimentary form, or not at all in certain an extensive territory is centralized at one point embodiments, but which require three or more and operated by one man, and in which superline conductors. visory indications or reports of switch and signal The present invention is applied to a control positions and of the occupancy of certain track station and controlled units distributed at am sections are transmitted to the operator for his number of substations along the railway. At a guidance in regulating train movements through typical substation there will be one power operthe territory. ated track switch, a group of semaphores or The functional requirements for such a systrackside signals governing train movements,

tem are similar in many respects to the requireand one or more track relays indicating occu- 15 ments for supervisory control of power stations, pancy or non-occupancy of certain track secand. some of the features of the invention are aptions or blocks. Some substations will have only plicable to such systems, but they difier in that signals and track relays, or other combinations. the controlled units involved in centralized traf- Three line conductors, common to all stations,

number of small groups scattered along a rail my preferred structure and transmit all necesway for a distance of many miles. Line circuits sary communications from the control station to involved in such a system are long and of relathe substations and vice versa. Signals are tively high resistance. Under these conditions transmitted from the control station and others economy dictates that control and supervision are received by the control stat o T e Signals. be accomplished with very few line conductors consist of characteristic impulses, and usually and with devices adapted to operate on the small of two or more successive impulses. Each imamounts of energy which it is practicable to pulse comprises distinctive combinations of positransmit over lines of relatively high resistance. tive and negative potential impressed upon two Furthermore, a large number of trains may be or all of the three line conductors. Twelve such 30 moving simultaneously through the district concombinations or distinctive impulses exist-sec trolled by the system. Prompt despatching of table below. Energy for outward impulses from all trains may require transmission of control the control station is derived from a battery at impulses and receipt of reports from the substathe control station. Energy the inward tions in rapid succession. Consequently rapid pulses to the control station is supplied by local 35 operation of the system is essential. Since the batteries at the substations of origin, and prefunits to be controlled are widely scattered and erably by the same batteries which supply local unattended except for periodic inspection and ener y for Operating track Switches d t maintenance, it is essential that only devices of side signals. T e followi table gives the 12 the utmost reliability be involved in the system. different characteristic impulses, and a arbi- 40 Comprehensionof my whole system and of trary numbering of them for convenient refer the description below of the detailed operation of ence. Upward flow in lines 1, 2, 3 will be called several embodiments will be facilitated by a genplus current and downward flow minus current. eral functional outline of my operating plan and The reason for this convention is more fully disof the characteristic impulses and calls or codes cussed below. 45

of those impulses that I use.

General functional outli Impulse #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #n #12 In a copending application, Serial No. 559,671,

filed August 27,1931,byl3lake andAdams,meth- H23 i i 1L 1 l 1 I *6 i 0 I so ods are disclosed for transmitting all necessary 0 v 0 control and supervisory information over a single line conductor with either ground or metallic Obviously each usable impulse must involve return by the use of time channels set up on -at least one line connection and one the line by independently timed synchronous i. e. such combinations as or +0+, or 55 outward and inward, are really initiated at the control station in a'recurrent program. Because the substation sends no inward signal except stations and only as they 0, do not complete .a circuit and cannot be used.

Apparatus at the control station is arranged to send out automatically a repeated program of signals or calls composed of successive impulses,

for selecting or making connection to each sub. station in turn. Each substation responds, of r course, to a different signal.

During this automatic program, if the dispatcher requires no change of track switch and trackside signal po:

sitions, each substation, when so called, responds automatically with a report signal giving an indication at the'control station of the position of 'its track switch, and trackside signal group and track relays. Thus all signals, both when called the possibility of conflicting signals initiated at different points does. not arise. Hence there is no need for the complex apparatus provided in some existing centralized traffic control systems for testing the lines for conflicting signals and, if necessary, for forcing report signals to await the transmission of already initiated control signals or vice versa.

Since report signals originate at the sub are called by the control station, the. ,need for up-to-the-instant supervisory information by the dispatcher requires that each substation be called at very frequent intervals. This is accomplished first by restricting the total code transmitted to and from 'each substation (calling signal plus responsive report signal) to five successive impulses, and

. second, by employing only apparatus adapted for .very rapid operation. Similar apparatus used in commercial printing telegraphcircuits is regularly operated at rates of forty impulses or more per second, and all the elements of the presentin vention are adapted to equal or greater speed.

.Hence, eight or more substations per second can be scanned for reports. This permits completing the whole program in a few seconds (e. g. in ten secondsfor a system of 80 substations) and close- 'ly approximates a continuous view by the dispatcher of the position of all supervised units.

' spond to the substation wanted, and'then presses If the dispatcher, however, desires instant control of or report from one particular substation, he may interrupt the automatic program, advance a call transmitter to call the desired substation, -.and send at once a control signal or receive a report signal.

Thereafter the automatic program resumes at that point. Normally, however, if a matter of ten seconds is not vital, when the dispatcher desires to make a change in the track switch and trackside signal set-up at some substation, he merely sets'to agree with the'dee sired set-up certainv control keys that correa control button. At the next automatic recurrence of the call for that substation, (i. e. some time Within ten seconds on an 80 substation system) the call will be so modified that the substation receiver 'will suppress, for that particular. cycle, the transmission of its report signal and will instead adapt itself to receive a control signal, (automatically sent right after the call), and ,to initiate the desired change in the track switch and trackside signals. At the conclusion of such 'a control signal the transmitter at the control.

station'is automatically restored to normal and the automatic program of scanning for reports is resumed.

Signal detectors at control station and substations may either be series devices responsive to current in the line conductors, or bridging devices responsive to potential differences'between line conductors. In the former or series arrangement my primary receiving element is a group-of polar 'relays in series in the control lines, selectively responsive to the' polarity of any current Local relays controlled'by flowing in the lines.

these line relays respond to specific ones of the 12 impulses also to specific sequences of such' impulses, in such a. way as toestablish difierent local circuits according to the signal received. In the latter or bridging arrangement high resistance polar relays, or an electronic equivalent, are connected across the different pairs of line conduc' tors, to control the local relays in a manner essentially similar.

The signaling cycle for each substation comprises a definite number of impulse periods. To fixthe ideas let us'here consider a particularem- .bodiment to be described below in which the sig- There might if we have a series of ten impulses, a, lb, c, d, e,',f,

h, i, '7', and if the first five (a b c d e) are a signal to substation No, land the remainder a signal to substation No. 2, it is necessary to insure, that no hybrid group of five impulses such as d e f g h will be improperly accepted as a signal by some other substation. For this reason certain impulse combinations are set aside as markers or impulse group starting impulses, and the sub station receivers are organized to respond only to groups of successive impulses initiated by, a

marker impulse.

As previously mentioned and shown in the table above there are twelve usablecombinations of positive and negative currents or potentials among three conductors. It will be noted in'the table that the first six combinations either have on line 1 with onlline 2, or vice versa, whatever may be on line 3, i. e., lines 1 and 2 are both alive and of opposite polarity. 'I'hese six are all the combinations in which lines 1 and2, alone, constitute a complete circuit, whetherline 3 is or is not used. As a; matter of structural convenience as will later be understood these six combinations are the ones used as markers.

In each of the other six combinations, numbers 7 to 12 in the table, the current in conductor 3 is a necessary consequence of the currents in conductors land 2. For example, in No. 7, with positive current in both conductors l and 2 the return current in conductor 3 is necessarily negative. With in line 1 and with line 2 dead, (N0. 11), the return current in line 3 must necessarily be etc. tions, 7 to 12, are fully defined by thecondition It' follows that these six combinar of conductors I and 2 only, i. e. by whether there is a plus current or minus current or no current in each. Use'is made of'this property, as will later appear.

As stated, the first, or marker, impulse for each signal is chosen from the firstsix combinations tabulated. This impulse, plus a second and a third impulse selected out of Nos. 7 to 12,

' constitutes the substation call. Since we have six options in each of three successive impulses 'we have available a total of 6 6 6=216 differbodiment, when one of impulses Nos. I to 12 has been chosen for the second impulse, only five choices remain available for the third impulse. Hence the total substation calls available in this embodiment are 6 6 5=130.

Of the available substation calls, whether there are 216 or 180, two are assigned to each substation. One is used to call a given substation when we wish that substation to send in a report signal. The other is used when we wish to set up the substation receiver for response to a control signal from the control station. Thus with the system to be described we can either call for supervision or call for control, a total of 216-:-2=108 substations; or in that embodiment mentioned just above we can call a total of +2=90 substations.

When the supervisory call of a given substation is sent, it causes a transmitter there to send in impulses that are indications of the conditions of track switch, trackside signals and track relays. These reports or indications sent from the substation comprise two impulses right after the three substation calling impulses. These report impulses, like the 2nd and 3rd calling impulses, are chosen out of the six impulses Nos. 7-12. Impulses Nos. 1 to 6, are used only, it will be remembered as first or marker impulses. Two report impulses, of which each is chosen out of six possible ones give us 6x6=36 available signals, which are just sufficient as shown below to transmit to the central office the information as to the positions of one track switch, one trackside signal group and two track relays. At some substations, having no track switches or trackside signals, only track indications are desired. The code described will indicate at central in such cases the position of five track relays.

Three different track switch conditions are possible viz: norma reversed and unlocked. Three conditions are possible for a group of trackside signals, viz: clear for westbound, clear for eastbound and stop. Two conditions viz: picked up or released, are possible for each track relay. The number of possible different combinations of these appa ratus conditions is therefore 3 3 2 2='36, or the same as the available different signals. In the case of a substation having only track relays we can supervise as many as five, for which we require 2 2 2 2 2=32 combined signals.

If we send out the control call, instead of the supervisory call, of a given substation, the receiver at that substation is thereby set up to receive a fourth impulse from the control station, which determines the desired set-up for track switch and trackside signals. The track switch may be desired at either normal or reverse. The trackside signals may be desired set to clear eastbound, clear westbound or stop. There are thus 2 3=6 possible combinations of controls to execute. The control impulse sent is chosen among the six impulse combinations, Numbers '7 to 12 of the table, according to the combined track switch and trackside signal setup that is desired. When a control call is sent, the fifth impulse period, used in the supervisory code as just described, is left blank.

Many variations of the operation plan and code automatic arrangements above outlined will occur to thoseskilled in the art, notably the following: Instead of positive and negative direct currents impressed on the conductors, we may use any two kinds of current, such as direct and alternating current, two alternating currents of different frequencies, different superposed frequencies, or pulsating currents of various characteristics. The essential point is that we must have (with such practical restrictions as the necessity of providing a return path for the currents), at least two current options, other than zero, available for each conductor.

If more than two current options or more than three conductors are available, the possible combinations constituting different impulses will be much more than twelve. If, for example, mam substations are concentrated within a limited region it may be economical to utilize a variant using more line conductors and less impulses per signal. For example, instead of the twelve combinations possible on three conductors as per table, four line conductors permit fifty usable combinations of positive and negative currents in one impulse. If fourteen of these combinations are set aside solely for first or marker impulses, there remain 36 others; thus groups of two impulses will give a total of 14 36=504 possibilities suflicient for six different calls for each of 84 substations. Thus all necessary call and control signals in a 4 wire system according to my invention can be conveyed in two impulses. One third impulse will provide the needed thirty-six different kinds of responsive report signals. Thus by adding one wire the number of impulses per substation reduces from five to three, and the supervisory program is greatly speeded up.

In another operating variant I do away with the automatic cyclic supervision of the condition of all R. R. apparatus that is controlled by the dispatcher, i. e. track-switches and trackside signals-retaining automatic cyclic supervision of only the track relays, because these latter, as the trains move, will change their condition independently of the dispatcher. Where this practice is judged satisfactory, and using a 3 conductor line, the report signal from the substation, which follows the supervisory call of three impulses, needs only one impulse instead of two,--because two track relays can have only four different combined conditions and there are available for this purpose six different kinds of impulseNos. '7 to 12 of the table. This operating varian cuts the total code per substation from five impulse times to four, and makes the supervisory program that much swifter. In this case the supervision of trackswitch and track signals is maintained as follows: when the control call of a substation is sent, followed by the one control impulse as outlined above, the automatic supervisory program i'ssuspended until the track switch and trackside signal have changed position in accordance with the control impulse sent." Then there originates at the substation a report signal indicating the completion of the changes ordered, which gives in front of the dispatcher an indication of the new -position of the controlled trackside apparatus.

The automatic program of recurrent supervisory calls for track relay condition then resumes.

In still another modification of my operating plan two substations may be arranged to answer the same supervisory call, and then each in turn to send in its report signal of two impulses, just as first outlined. "Thissaves the supervisory call of every second substation, i. e., it cuts the total 'code'for two substations, in the automatic program, from ten impulses to seven. In this plan, there is an individual control 'call per substation followed by one control impulse, the combination determining one of six combined track switch and trackside signal conditions, all as outlined Since. there are 216 difi erent calls and since in this variant plan there are needed for every two substations two control calls but, only' one supervisory call, or 1% calls per substation, it

. is evident that instead of 108 substations as many as '216+1 =l44 substations can be handled.

. Other modifications of my preferred use of codes and operating plan may be made by' separating or distinguishing from each other the codes or groups of signals intended for individual substations by a mere. pause or time lapse, in-

impulses for every purpose.

between codes, only two impulses, each of which stead of by specially. set aside marker impulses. These modifications give the option of all twelve Thus, using a pause may be, any one of the twelve, would give 12x 12:144difierent calls. The pause, however,

must consume about as much time as one more impulse. 7

Still other -modifications are practical using more or less than the first outlined number of six marker impulses.

In other variants the calling codes may be restricted entirely to the use of the marker impulses. ln which case if, as before, we use the first six combinations of the impulse table as markers, 6 X 6 X 6:216 would still be the number of calls. In that case the control and report signals would use, as before, only the other combinations.

Description Referring to the accompanying drawings, Fig. 1 shows schematically three line conductors with series line circuits, and their relation to the controlstation and substations, and indicates typical resistance values for certain elements;

Fig. 2 shows schematically multiple line circuits operatively equivalent to the series circuits of Fi 1; c c

Fig. 3 shows in detail the apparatus and connections at the-control station according to one embodiment of the invention; 7

Fig. 3a shows in detail the connections and apparatus at a substation, cooperative with 'Fig. 3;

Fig. 4 shows part of the connections at one substation in a modified embodiment.

The same reference numerals are applied in all drawings to elements which are identical or functionally equivalent.

Before describing the localcircuits and operation in detail we may first consider the line circuit and the basic signaling conditions over the' threelines of my preferred structure, with both serial and bridging arrangements of line relays and with particular reference to the adequacy of the signaling energy.

Fig. 1 shows the serial arrangement of line relays in three lines H, [2, and I3 extending from a control station through a long series of substations, of which three are illustrated. At the control station the three lines are 'joined in' Y as by a'bus connectionIlO. At theremote end they are Y connected through resistors 40 to another common point. such as bus 14, so that they constitute .a' three-wire circuit Y'connected at a both ends. Between bus connections I 0 and I4 each line passes serially through one of polar control station.

relays 21,222,,23 .at the control station and through one of polar relays 3|, 32, 33 at each substation."

All of these relays are biasedto close a central contact when deenergized, a right-hand contact when energized by positive current, and. a left- 7 hand contact when energized by negativecurrent. Thus, each relay is adapted to close three distinctivelocal circuits according as the current through its winding and the associated line'clrratus and connections not shown in Fig. 1 con- .stitute the receiver at the control station for'report signals transmitted from the substations. In

like manner the three line relays 3|, 32, and 33" at each substation, together with associated local elements, constitute the substation receiver for calls and control signals transmitted from the Branch circuits connect the lines H, l2,"and

i 3 to a transmitter 20 atthe control station which" establishes suitable connections at certain 'times to the positive and negative poles of battery-24 for transmitting call and control signalsgfand similar branch circuits at each substation connect the lines to a transmitter30 which estab-' lishes connections to the terminals of a local battery Mffor transmitting supervisory signals. Transmitters 20 and 30 are merely indicated in Figj i. to convey their functional relation to the line circuit. They are shown in, detail in ,Figs. 3and3ak V 1 In an actual application the control lines ll, l2, and I3 may extend a hundred miles or more and may have a resistance of 500 ohms per conductor, exclusive of relays. Each line may include one hundred substation relays in addition to one control station relay and a terminating resistor at the remote end. As indicated in Fig.

1. I prefer to wind the control stationrelays fer about 1000 ohms and the substation relays for about 5 ohms, and to use terminating resistors a of about IOOohms. The control station battery 24 may have a potential'of 200 volts. Under these conditions, if the transmitter 20 connects battery 24 between lines H and I2, current will divide two ways. One portion, flowing through the 1000 ohm coils of control station relays 2i and 22 and the adjoining bus connection, constitutes a slight drain on the battery but serves no useful'iunction in transmitting signals to'the substations. The other portion, flowing to'the left in Fig 1, will traverse two line conductors of some 500 ohms each, two hundred of the 5-ohm 2200 ohms. Under these conditions the line current will be about 0.09 ampere and'the energy available to operate each' substation line relay will be 0.04 watt, Which'is ample for operating a station batteries for the latter purposes have a potential of the order of 20 volts.

When this relays and two 100-ohm resistors, a total of some '55 voltage is applied between conductors II and,

l2 at the most remote substation a small useless current will flow through two of the 1-00 ohm resistors 40 and the bus connection I4. ,Signalmg current will fiow to the right through two line conductors, two hundred S -ohm relays and two IOOO-ohm relays. The aggregate circuit resistance is 4000 ohms, the current 0.0105 ampere,

and the energy expended in each control station relay 2| or 22, 0.025 watt, which is ample. The energy expended in each substation relay is very small, but as will be later seen it is immaterial Whether these relays respond to the reportimpulses or not.

In certain cases (impulses Nos. 1, 3, 4, 6, '7, and 12 cf the table above) signaling current will fiow out through one line conductor and back through the other two conductors in multiple, or vice versa. In these cases the current in each of the two conductors in multiple will be less than for the above simpler case, but will still be ample for operating suitable relays.

Fig. 2 shows schematically the multiple connected or bridging equivalent of the series system illustrated in Fig. 1. One control station and two of the many substations are illustrated. As in Fig. 1 the lines extend through the control station and each substation, but are notv joined at their ends by busses l and I4 as in Fig. 1. Transmitters 2e and 30 and batteries 2 3 and 3 2 are functionally the same as in Fig. 1, although much lower battery voltages may be employed. In place of each of the relays 2!, 22 and 23, and 3!, 32 and 33 of Fig. l serially connected in the three lines there are at the control station and at each substation a pair of electronic relays such as ZIX, 293? connected between each pair of line wires. There are thus at each station three such pairs delta connected between the line wires. Since this is purely descriptive of line conditions the local circuits in the plate circuits of the electronic relays are omitted. A source of alternating current, not shown in this diagram, is required at each station for energizing the plate circuits of the electronic relays.

Since all the pairs-of electronic relays, 2 IX and MY, 22X and 221 23X and ZBY, SIX and SIY, 32X and 32Y, 33X and MY are connected alike between their respective line wires it will sufiice to describe the operation of one. The grid of relay 25X and the filament of relay ZIY are connected to line i l, while the filament of relay 2M: and the grid of relay 2ly are connected to line l2. A suitable grid bias battery is included in each grid connection. With this arrangement three conditions equivalent (though, not identical) to the three positions of polar relay 2| (Fig. 1) may be established in the local plate circuits controlled by electronic relays 2M: and Ely: (1) if line H is positive with respect to line i2, thus establishing a positive relative potential on the grid of relay 2|:r, pulsating current will flow in the plate circuit of that relay while current in the plate circuit of relay My Will be blocked by negative potential on its grid; (2) if line H is negative with respect to line l2, current will be blocked in the plate circuit of relay 2!.r but will flow in the plate circuit of relay 253 (3) if lines H and i2 are at the same potential, the negative potential maintained by the bias batte y in each grid circuit will block the flow of current in the corresponding plate circuit. Thus, in place or three local circuits closed selectively in accordance with current flowing in line H, as in Fig. 1, we have two local circuits closed or not closed selectively in accordance with potential diiierence between lines II and l2j but in either case we have three distinctive responses in the local circuits, according as current or potential is positive, negative or zero. In Fig. 2, these three local conditions are: (1) flow in plate circuit ofv relay 21:0; (2) flow in plate circuit of relay Ely; and (3) both plate circuits blocked.

While I have shown and described below only such local circuits'as are suited to cooperate with the three position series line relays of Fig. 1, which is my preferred line arrangement, it will be readily understood by those skilled in the art how these local circuits may be modifiedto perform identically under control of the three plate circuit conditions mentioned.

Within certain limitations as to line resistance and number of associated substations it is feasible to replace each pair of electronic relays in Fig. 2 with a three-position polar relay like those shown in Fig. 1, except that the relays should be wound for high resistance. The required resistance of the polar line relays becomes prohibitively high, however, when the lines are very long and the substations very numerous; for example, under the same conditions as the numerical case previously discussed for series line relays, the optimum resistance value for delta connected polar relays would be about 80,000 ohms. This arrangement, however, becomes practical for small systems.

In the multiple connected line circuit arrangement of Fig. 2 it may be noted that, while the number of different combinations of positive and negative potentials on lines ll, l2, and I3 are the same as in the series arrangement of Fig. 1, the particular combinations for any given relay response are diiierent. In other words the correspondence of line potential combinations and relay response combinations is different. Thus, in 1, on line H and on line [2 puts relay 3! on its right hand contact, relay 32 on its left hand contact, and relay 33 on its central contact. A logically corresponding relay response in the Fig. 2 structure would be flow in plate circuit of electronic relay Elm, (3Iy blocked), flow in plate circuit of relay 3% (32:1: blocked) and relays 33a: and 33g both blocked. But the arrangement of battery potentials on the three lines necessary to get this corresponding result is on both lines ii and i3 and on line l2 instead of on line ii and on line it. The following tabular arrangement shows the correspondence of the potential differences across the three delta connections with the twelve line potential combinations of the original impulse table. The potential differences are taken in the direction stated, e. g., for combination #1 the potential difference line 1 to line 2 is given as negative, meaning that the potential falls when going from line 1 to line 2, or that line 1 is at the higher potential. This tabular arrangement is shown to facilitate the practice of my invention by those preferring the branching line circuit.

Impulses 1 2 3 Line current (series):

Linol 1.l-++00- L111103 .+0+0- Potential difference (bridgi Line3tol o++ Opcmtz'on.Fig. 3 shows in detail the apparatus and connections at the control station,

erative functioning of the sub'sta ti'on Fig. 311 'being at first merely assumed. The cooperation of ra ns and elements and connections to the right of L-L are individual, i. e., one such set is re.-

quired for every cooperative substation. The

j reference numeralslof all parts of the apparatus and elements individual to substations bear small lettersuffixes ((8,1), 1) corresponding both to designations of thesubstations they serve and to'the positions or contacts 10., 1b etc., of

common dial 'switch- 1; which latter switch by its. position determines with which substation com- 7 munication is being held; as will be seen. The

substation shown in Fig. 3c, and to which the most of the individual apparatus and parts shown in Fig, 3 corresponds, is the one I have designated a. 7

'1 There are fourphases of the control station operation to be described:

(1) The cyclic automatic transmission on lines H,. 12, and 13 of supervisory calls for each substation in succession. It will be remembered that these calls comprise three. successive impulses, starting with one of impulses Nos. .1 to 6 reserved as markers.

(2) The reception, immediately after the three outgoing supervisory call impulses, of two successive incoming or report impulses, recording on suitable indicators, such as lamps, the condition of the R. R. apparatus at the called'sub'station.

' (3) The manually initiated alteration of the next supervisory call for any given substation into the control call for that substation.

.(4) The outward transmission immediately after sending the three impulses of a control call fora given substation of a manually predetermined control impulse, (one of 'six options) to eflect desired changes in R. R. apparatus at that V substation. j j i Phase (Di-Dial switches 25, 2B, 21, 28, and 29, respectively comprise rotating wipers 25', 26, 21', 28, and 29 and five stationary contacts each. These contacts will herein be designated by the switch numeral'followed by the positional number of the contact. Thus contact '25-2 refers to contact numbered 2 in dial switch25, Wipers -25 to 29' are'flxed on a common shaft S. -Any well known driving means of reasonably constant speed drivesshaft S at a speed which may be of the order of 8 revolutions per second or 430 R. P; As will be seen later the speed of this shaft determines the length of the various impulses, and the operating a operating substation on lines II, l2, and [3,

which may be aconsiderable number.v Thereis at the control station a battery 24, shown in Fig.

1. As stated above in connection with Fig. 1, battery 24 rnay have 200 volts. A connectionis contacts jSa-I,

rentdownward will be called current.

made to its mid-point, which point may beybut'i is not necessarily,- grounded. To avoid multiplicity'of lines inFigs. 3' and 3a-all contacts and wirestowhich there is a permanent battery connection bear a a or a ground symbol to denote connection respectively to the, positive or negative poles or to the mid-point of alocal It will be understood that in Fig; 3a

battery. the and symbols represent permanent con.- nections of the substation battery, which is batcontrol station battery 24.

tery 34 (see Fig. 1)' of lower voltage than the- Wiper 1', as indicated by the sign,-is con-, i

shown in its operated position; It shortly will be seen that relay 6a,.by means of the particular and dead connections of its contacts, determines'the sequence of impulses that'will be put on lines ll, l2, and I 3 by dial switches 25, 26, and 21. In other words relay 6a embodies in its contact connections the supervisory call for substation a. It will be understood that relays 6b, G0, etc., just like to except having dif! ferent battery connections on their fixed. contacts and thus embodying each the call for a different substation, are connected respectively to contacts 1-b, 1-c l-f of switch 1. In the drawings the sixteen branch connections to 6a-2, fizz-l6, designated m; -m, show where the multiple connections are made to the moving contact members of the other'relays 6b, 6c, etc.

The lower twelve moving contact members Ga-l, .6a-2,'. Gar-I2, of relay 6a, are connested in that order: to dial switch contacts 25-4, 25-3, 25-2, 25-l; 26-4, 2B3, 26-2, 25-h.

21- 1, 21-3, 21-2, 21-i; wipers 25', 26', and 21 are connected by wires 25", 26", and 21" to lines 'll', l2, and I3. With relay 6a operated, when wipers 25', 26, and 21' reach contacts 25-1, 26-I, and 21-! it willbe seen that lines H, i 2, and 13 will be connected respectively to contacts Bw-4,'6a.-8, and Ba-IZ of relay 6a and hence respectively to the and poles of battery 24.

It is here convenient to adopt a convention as to what will be meant by current and cur rent in the lines, and as to the response thereto of the polarized line relays. Current flowing upward in iines ll, l2, and 13 in Figs. 3 and 3a will be'called current in these lines, and our- The various polarized line relays, 2Ia, 2lb, 22a, 22b, 31a, 32a, and 33 in Fig. 3 and Fig. 3a, will be understood to move their armatures to the right on current and to the left on current, and on 0 current to resume or retain the positions actually shown.

This convention is necessary because battery potential applied tofa line,

at one 'side' (say above in the drawings) of a.

given polarized line relay will have one effect thereon, andthe same potential applied to the same line at the other side (say below) of the same relay will have an opposite effect. In this F connection, We have'shown'the control station atone end of the, lines,but in practice the control station often may be in'the middle of the group of substations it controls. It isthus evident that, in' the series line arrangement, the

twelve characteristic impulses must be described, not by the potentials placed on the lines, but by the currents resulting in the lines.

The connections just traced, of battery to lines I! and i3 and battery to line 12, result in current upward in lines ll and i3 and downward in line l2, which by the convention and for operation of the line relays is called on line ll, on line I2 and on line l3. By reference to the basic impulse table hereinbefore shown this is seen to be impulse No. 1,. one of the six option reserved for marker or firstof-group impulses. It must here be assumed, to be elucidated, that all substations require one of these marker impulses tobe able to start to respond to a call, and that only certain ones (in a full system, only one out of every six substations) will start on this particular marker inipulse.

Now as shaft S turns farther, wipers 25', 25,

2'! leave contacts 25-l ZS-l, 21-l respectively, and after a brief period of no connection pass onto contacts 25-2, 26-2, 21-2 which, since relay 6a, is still operated, connect lines l I, I2, and I3 respectively to contacts Ga-S, 60-1; and Ba-ll which are connected to dead, and By the convention, this gives as the second impulse 0 and current in the lines to the substations which constitutes impulse No. 11 of the table. This is one of those reserved for all but marker uses. It must be assumed-and will later be elucidated-that of the substations able to start receiving the call that began with the No. 1 impulse only certain ones (not over six) will be able further to'respond to this particular second impulse of the call.

- As wipers 25, 26, 21' pass to contacts 25-3, 26-3 and 21-3, it will be seen that lines II, l2, and I3 are connected, respectively, to (l, and battery, which by the convention gives .0, current in the lines to the substations. This is impulse #10 of the table. It must be assumed, to be later shown, that of the stations able to respond to both the first (marker) impulse and the second impulse O only one will respond to this particular third impulse, and that that one will respond by immediately putting on the lines a fourth and fifth impulse (both chosen out of impulses Nos. 7 to 12) reporting the condition of R. R. apparatus at that substation.

Phase (2) .-The two report impulses, initiated at the called substation in response to the supervisory call whose transmission on the lines was just described, occur in the fourth and fifth impulse periods, which means while wipers 25, 26' 29 are on contacts 25-4, fiE-G 29-! and then on contacts 25-5, 26-5 29-5. Considering first the fourth impulse period, it is understood that in this period the called and responding substation may put on each of lines ll, l2, and l3, either battery, battery or 0 battery, within the optiens offered by impulses Nos. 7-12 of the table. In this fourth period,-since we are considering now only the supervisory call and report impulses-contacts 25-4, 26-4 and 21-4 will be found dead because'theirconnected contacts fiat-l, ta-5 and 5a-9 lead to open back contacts Ella-5, 5|a-3 and 5|a-2 of a locked-up relay 5|a, whose function will later be described. Therefore dial switches 25, 26, and 2'! in their fourth position cannot transmit or receive any current combination or characteristic impulse to or from lines ll, I2, and I3. This is also true in the fifth position because contacts 25-5, 26-5 and 21-5 are permanently dead. Dial switches'28 and'i whose contacts 28-l,

28-2, 28-3, 29-I, 25-2 and 29-3 are'permanently. dead-dead contacts in the dial switches are'indicated for quick recognition by black circles-clearly could not send or receive line impulses until the fourth position. But in their four and fifth positions wipers 28 and 29' pass off these permanently dead contacts, and-it will be seen-serve to convey to the proper indicating apparatus the indications of the report impulses put on the lines by the responding subteries, usually available at the substations withr out extra cost, have relatively low voltage-batteries 34 shown in Fig. 1 it is stated may have 20 volts-the polar relays at the control station require to be especially sensitive. I therefore prefer, in practice, to replace at the control station each three-contact polar relay, like 2| or 22 of Fig. 1, with a pair of two-position and two-con tact polar relays in series. These may thenbe of printing telegraph type and exceedingly quick,

reliable and sensitive. contacts so interconnected as to close three different local circuits according to whether or 0 current is in the line. In line I! relays 2 IA and ZIB constitute such a pair. Their coils are in series; They are so biased as to assume the positions shown when no current is in their coils. They both have their armatures to the right when -lcurrent (i. e. upward current) is in line H. They both have their armatures to the left when (i. e. downward) current is in'line H. As shown, with 0 current, the mid-point of battery 24, represented by a ground symbol, is connected through right hand contact of HE, through armature of ZIB, wire 2| and left contact of 2|A to the armature of 2|A. With current in line i l the armature of 2 IA moves to the right and connects to pole of battery 24.

With current in line H armatures of HA and 2|B will both be at the left and the pole of battery 24 will be connected through armature of HE, wire 2| and left contact of. HA

Each such pair have their to the armature of 2IA. Wire 28" is connected to armature of MA and is thus'connected respectively to the midpoint, the pole or the pole of battery 24 according to whether 0- or currents are in line H.

In line l2 the pairof sensitive polarized twocontact relays 22A and 22B are similarly interconnected to perform the function of one threecontact relay like 22 of Fig. 1. With 0 current in line :2 the armatures will be as shown, connecting wire 28", through right contact and armature of 22B to wire 22, left contact and armature of 22A, to wire 29". With current in line l2 the armatures will both beto the right, and that of 22A thus connects wire 29 to battery. With -current in line l2 both armatures are to the left, connecting the battery of the left contact of 223, via wire 22' and armature of 22A, to wire29". Thus wire 29 is connected either to wire 28", to

whether current in line 12 is 0, or

- pole of to poleof battery, according Wires28" and 29""lead'respectively to wipers 28. and 29 of dial switches 28 and 29. In the fourth impulse period wiper .28 is on' contact.

28-4, which isiconnected via contact 6a l4 and wire 55a to junction point 55a of indicator circuit 55a" (shown enclosed in a dotted rectangle). Wire 5511' may,{ if ,desired be wired through a contact la6, of relay 5la (shown in a dotted circle) forreasons explained below- For the present description, relay 5!;a being locked in operated position, contact 5la6 (if presentlis closed and may be, disregarded.

Similarly wire 29", through wiper 29, contact 29-4, contact Bal.6 and wire Ilia leads'to the relay Isa. A closed contact Sic-J (shown in a dotted circle) may or may not be inwire l9a' for reasons to be disclosed. Relay I Be with:resistance 41a and lamp 46a constitutes another indiy 7-12. It was pointed out above, in connection withtheimpulse table that this group of six impulses is fully defined by the current in lines I and 2-or, as they are designated in Fig. 3, lines II and I2. The current in the third line is predictable from the currents in lines H and I2; It is my choice of the report impulses out of the group having this property that makes it unnecessary in the Fig. 3 structure to use any line relay or relays at the control station in line l3. Line relays'are shown in all three lines of the Fig. 1 :line circuit because'that is a more generalized showing in which advantage was not taken of this property of certain impulses. To obtain symmetrical current distribution it is preferable to put a resistance'56 inline [3 equal to the resistancefoi a relay pair 2|A, H3 ,or 22A, 22B."

Impulse numbers 7 to 12, by the property mentioned, reduce to the following six different combinations of currents in (not polarities on), lines II and I2.

Impulsenumber 7 8 9 10 11 12' Line 11 o 0 Linel2 o 0 Considering the battery connectionsof wires 28 and 29" when a substation responds, as it may, with any one of these impulses, we find that, the linerelay circuits already traced give the following results: 7

Connection Connection Impulse of wire of wire 28" 29" 7 pole Once energized relay |9a closes a locking circuit by its contact through resistance 41a to battery; and lamp 460. will remain lighted until relay l9a is again unlocked. This may signify that track relay #1 is operated.- If relay l9a is once locked up,.e. g. by a No. '7 report impulsefrom thesubstation in the fourth period, the next time in the cycle of dial switch 1 and of dial switches to 29 that'wiper 1' is on contact 1a and that wiper .29 is on contact 29-4 thesame substation may send in the same or a different report impulse. If it is one of Nos. 7, 9 or 11 relay |9a and lamp 46a will not change, if it is one of numbers 8, 10 or 12 wire 29" becomes and relay I9a is shortcircuited and falls putting out lamp 46w. This may signify that I track relay #1 is deenergized. This condition in turn will persist until the corresponding substae tion again sends in, in the fourth period one of impulse Nos. '7, 9 or 11. Thus, as regards lamp 46 there are only two kinds of report impulses,

those that light it andthose that put it out. Both 1 7 kinds are receivable only from one-particular substation, only in the fourth impulse period, and

only after the three impulse supervisory call of that substation has been sent. One kind maybe given the meaning that track relay #1 isener- I gized and the other that it is deenergized.

Since-for each one of these two kinds of reports about track relay #1 there are three diI-. ferent actual impulses differing by the potential they place on wire 28" it is clear that the potentials on wire 28" may be used to indicate any other three conditions at the substation, inde-,

pendent of the track relay. Such may be: track' switch normal, unlocked, or reversefl Via contacts 23-4 and Err-14 and wire 55a, as traced, the potentials of wire 28" are extended to junction point 55a of indicator circuit 55a. From this point one relay Ila is branched to battery with a relatively high resistance I521. in V series and another relay l8a is branchedg'to battery withan equal .resistance I6a in series. Two relatively low resistances Ma and 4211 also branch from this point 550. to and battery respectively, but their circuits are only closed through theback contacts of relays 1m and lfla' respectively.

In operation, relays Ila and I8a are never both deenergized; they may be both energized or either one alone may be energized. Whatever their condition, if wire 28" is made (impulses Nos. 7 '7 or 8) relay Ila. and resistance I 5a'will be shorted and the relay will fall, (if up), while relay l3a will be operated by the following-circuit; battery, winding of relay I But, resistance iEa, junction 55a. and to battery as already traced. When relay llaiell it completed by its back contact a circuit from battery through low resistance a; to junction 55a. As long as junction 55a is' no current flows in this low resistance circuit, or, through relay Ila. When wiper 28' leaves contact 28-,-4, junction 55a is cut off. from. battery, and current flows in parallel through relay "it plus resistance 15a and through resistance 4 la, then in series through resistance 16a and relay l8a. This current. holds 7 up relay l8a as the parallel circuits mentioned amount to a quitelow resistance. Of the total flow the greater part takes the path through resistance 41a, sothat the current through resistance I5a and relay l'la is insufficient to operate the latter.

If wire 28 and hence junction 55a are the operation is exactly as just described except that it is relay lla that operates and locks up, and relay lBa that releases and so heavily shunts itself by the low resistance 42a that it does not operate in series with Ila.

If, now, wire 28" and hence junction 55a are connected to the midpoint of battery 24, junction 55a comes to a potential halfway between and of course, and both relays Ila and H311 Will be energized. When wiper 28 passes off contact 23& and disconnects wire 55a this makes no change in the potential of junction 55a, both relays remaining energized from battery to battery in series respectively through resistances lfia and Ilia. The circuits of shunt resistances lla and 42a are, of course, both opened by the energization of both relays. This condition will persist until junction 55a is again made or via circuits already traced. Lower contacts of relays lla and I80. cooperate, as is obvious, to light selectively lamp 43a, lamp 44a or lamp 45a according as relays Ila and la are both operated, 93a operated with lla deenergized or l'ia operated with lBa deenergized. These lighted lamps may for instance, mean respectively track switch unlocked, normal and reversed.

With the assumed meanings of lamp 46a and of lamps 43a, Ma, and 45a the following becomes the meaning of the various report impulses sendable by a substation in the fourth period:

Lamps Track Lamp Track relay Impulse lit switch 46a #1 441: normal lit energized. 4411 o out. deenergized. 43a unlocked lit energized. 43a do. out deenergized. 45a reversed lit. energized. 4501 .do out deenergized.

These are arbitrary meanings, given only for illustration. Lamp lfia lit might equally well mean track relay deenergized, and hence block occupied. Any one of lamps Ma, Ma, 65a may, instead, be assigned to mean trackside signals set for eastbound proceed, stop or westbound proceed.

In the fifth impulse period, as stated above, another set of indicator circuits like'lsa" and 550." may be connected through contacts lia-l 5 and lid-l3 respectively, and used to record reports, say, of the condition of track relay #2 and of either a track switch or a set of trackside signals.

Wiper l, normally stopped by a cam on shaft S, is frictionally held on its own shaft and may be manually moved at once to any contact by the despatcher. This deenergizes the particular relay 6a, Eb, etc., that may be up at that instant and energizes the one corresponding to that contact of switch 7 to which he moves wiper 1''. In this way the dispatcher may cause the supervisory call of any desired substation to be sent out at once and may receive its report signals without waiting for the completion of the automatic cycle. For supervision, i. e. obtaining reports, this facility would however, rarely be used. On occasion this ability instantly to call a substation out of turn may be useful for sending the control calls and controlling impulses about to be described.

Phase (3).The control call for each substation is conveniently, and as shown in Fig. 3, so chosen that it differs from the supervisory call of that substation only in using a different third impulse. This is, however, a mere matter of convenience. Of the 6 6 6=216 or 6 6 5=180 diiferent substation calls outlined above as possible with three successive impulses on three wires, any two may be chosen as respectively the supervisory and control calls for a given substation. As shown the difference between the supervisory and the control call results from releasing relay 5 la by pressing key 520., thereby opening the locking circuit that passes through front contact 5lal. Parenthetically, before sending out a control call for any substation, e. g., the a substation, the despatcher must have set the switches 53a and tea of that substation to sendthe required controlling impulse right after the control call. The function of these switches will be later described,--the present point is that the release of a particular relay em or 5), etc., by its key 520. or 52?), etc., alters the supervisory call of the corresponding substation to its control call, which must never be done until the control impulse sending device has been set as desired, since some control impulse automatically goes out immediately after the control call. Resuming consideration of the control call itself, in the particular embodiment disclosed and for the particular substation, a, of Fig. 3A, the third impulse of the a supervisory call was above seen to be 0, i. e., current in line H, current in line I2 and in line 13. It is 0 in line H because there is no potential on contact Ba2 to which Wiper 25 connects line H in the third impulse period. By releasing relay la it is seen that'com tact 5la4 puts battery on contact 6a2 and hence on contact 25-3, (causing downward flow in line I I) changing the third impulse of the call from 0, to in lines ll, l2 and I3 respectively.

It must be assumed, as will later be shown, that the called substation will respond to this altered call by preparing to receive and to act upon a controlling impulse sent from the control station in the fourth period, instead of by sending back report impulses in the fourth and fifth periods.

Phase (4) .The controlling impulse, as stated herein before may be any of Nos. '7 to 12. What it actually is depends upon the battery connections made to lines ll, l2 and [3 by wipers 25, 26' and 21 as they pass over contacts 25-4, 26-4, 21- 3. through contacts 6al, ta-5 and 6a-9, respectively, to contacts 5la5, Eula-3 and 5la2, which are now closed since relay Elm was unlocked by key 52a. Wires 53a and 53a" connect contacts 5la-3 and 5la-2 to the upper and. lower levers of double throw two pole switch 53a. Wire 54a connects contact 5la.-5 to the second brush from the top of commutator switch 54a. The latter, which is shown in development, isa small rotary drum type commutator or pole changer with three positions A, B, and C and ten brushes, and turned by knob 54a". Any equivalent device for altering circuit connections may be substituted. In the positions'show'n of both switches battery from the top brush of 54a is on wire 54a. Wire 53a is dead. battery from the seventh brush of 54a is on wire 530.".

These contacts are connected,

This brings 0 and. potentials respectively tion C gives impulse No. 7. If wenow throw switch 53a to its lower position we find we get impulses-Nos. 12, 10, and 8 corresponding again to positions A, B, and 0,01? switch 54a. 'Thus by setting the two switches we are able to determine. the, sending as a fourth impulse of any desirejd one of impulses numbers 7 to 12. As will later be seen the impulses 11, 9, and 7 sendable when switch 53a. is as shown, i. e., toward the side marked N,'may all be. used to control the track switch at. the cooperating substation to assume itsv normal position. The. other three impulses, Nos. 12, 10 and 8, sendable when switch 53a is down, or toward the side. marked R, may, all conveniently be used to cause the track switch to go tofreversed position. Due to time of shifting,

- and accidents, a track switch may actually be l possibly stuck) andreversed.

foundand reported in one of three conditions, namely normal, unlocked (i. e. moving or There is, however, never occasion to control itto move into other than the .two positions, namely normal and reversed. This explains the need of three different reports for' a track switch with only two different controls.

The two control impulses sendablewith switch 5411 at position A may both'conveniently be used to cause a tra'ckside signal. setting for proceedeast bound. The two sendable. withv 5.4a at B may both set signals for stop. .The two sendablewith 5.4a. at C may set signals for proceed west bound.. Thus, with my preferred choice. of. impulses, the despatcher may independently control a track switch by setting 53a and a set ofv signals by setting 54a.

'Clearly' relay 5m, when unlocked by key .52a'to send the control call of substation w and to send thereafter the desired controlling impulse. as just described, must be energized and locked up again before thejcycleof calls again comes to substation a, i. e. before wiper I of switch! gets around again to contact 1a. This is conveniently done by connecting the upper or operating winding of relay 5m to any contact of switch I that is passed over by wiper 1" after leaving contact Ia and before again getting around to it. In the drawings the operating winding of relay Sin is shown con-' nected by wire 6b" (leading also to relay lib) and by branch wire 5la' to contact lb. Thus as wiper 1' comes on contact 1b and energizes relay 6b to send thecharacteristic call of substation b it also energizes the operating coil of relay 5la. The latter, if deenergized by key 52a, then pulls up and locks itself up by its contact 5 la--l and its lower winding, ready'to be deenergized again by key 52a the next time the control call of substation. a is sent. Similarly relay 5lb corresponding to substation b is energized on contact 1c in parallel with relay 60, etc., etc., completing the circle,

the last relay, 5| is (as shown) energized by wirev wireia by which relay 6a 5| jbranching from is energized.

The contacts '5ld6 and 5|d-1 are optional, as suggested by the enclosing dotted circles. The

' control station line relay pairs HA and. B, 22A

and B not only respond to report impulses coming from a called substation but also to the impulses sent out from the control station. The first three contacts of dial switches 28 and 29, being dead,

prevent any eil'ect on indicator circuits l9a and 55a" of the three impulse supervisory calls or control calls that are sent out. When, however,,

a controlling impulse, e. .g., for substation 41, goes out in the fourth period wipers 28' and 29- will be on contacts 28-4 and 29-4, which are not dead, but lead by wires 5501- and I90. to indicator circuits 55a" and l9a'f. not interrupted, false'indications may result on the various lamps corresponding tov substation a. This is of no import practically since the despatcher knew the substation conditions just before he pressed key 52a, knows that he is sending a controlling impulse, and knows that in less than a cycle, 1. e., within seconds or so, the correct indications will again be continuously shown, including indications of any changes. his controlling impulse has caused. If desired, however,

by adding to relay 5la. the two contacts 5Ia-6 (2) The responsive sending out of the two re-.

port impulses;

(3) The reception of a control call;

(4) The reception of a controlling impulse.

after a control. call.

Phase (1 ).-As was shown in detail the supervisory call sent by the control station apparatus for cooperation with substation a comprised impulse #l as marker followed by impulses #l I and then 4%).

may be expressed thus: 1st +1 2nd U 3rd, 0 At the substation, instead of such three-contact polarized line relays as are shown in Fig. 1, or the pairs of two-contact polarized line relays shown at'the control station, I have used an equivalent but more inexpensive arrangement of one two-contact polarized relay and one neutral relay in series in each line in which three different current conditions have to be deter-' substations is desirable because there are so many,

and is possible because they only have to respond to. impulses from the high voltage control station If wires 55a and I9a' are.

According to the convention, i. e.,' in'- terms of current in lines ll, I2, and Hi, this call battery'. In line H relay 3IA is a centrally biased polarized relay. Its armature moves right on plus current and left on minus current, and returns to center on 0 current; Relay 3lBis an ordinary fairly sensitive relay with one back contact which it opens on current of either kind in the line. The armature of 3IA is permanently connected to the positive pole of a local battery 34, which may be the same as used for operation of local railroad apparatus. The armature of relay 3IB, through its back contact, is also connected to plus battery. Thus if 0 current is in line,

lithe armature ofrelay 3H3. supplies a plus p0.-

. to wire 51.

tential to Wire 58 connected thereto. If. plus current is in line H, 3IB opens, its contact and disconnects wire 58 from plus battery, but 3IA applies plus battery to its right-hand contact and If minus current is in line II, 3IA applies plus battery to its left contact and to wire 59. Thus one of wires 51, 58 and 59 is selectively connected to plus of local battery 34 according as line II carries 0 or current.

It is seen that the connections of relays 32A and 323 in line I2 are similar, selectively connecting wires 61, 68, and 69 to minus local battery (instead of plus) according as current in line I2 is 0 or As will shortly appear local relays BI, 62, etc., are variously connected between one of the group of wires 51, 58, and 59 and one of the group 61, 68 and 69, whereby the selective wetting of one wire of each group selectively operates these local relays. I

According to choice of impulses for substation calls certain substations might require a pair of relays like 32A and 323 in line I3. As I have chosen them, however, in this preferred showing, there is never required in line I3 at any one substation means to distinguish between three current conditions, but only means to distinguish one current condition from the other two. At the group of substations that includes substation a, there is only one polarized relay, 33, in line I3, having one contact that is closed when there is plus current and that is open otherwise. At other substations the corresponding relay to 33 will be a polarized relay, required to close one contact, only if current in line I3 is minus. At still others it Will be a neutral relay required to close a contact only if current in line I3 is 0, and to open the contact otherwise. The resistance of the relay in'line I3 at each substation is preferably made equal to that of the pairs like 3IA plus BIB and 32A plus 323; or a special resistance coil may be inserted in line I3 in order to get symmetrical current distribution in the lines.

Reverting to the specific substation shown, when there is plus current in line I3, relay 33 connects wire 69 to wire Ill. Wire 69, it was seen, is connected to the local battery (namely, the minus pole thereof), only on the left contact of relay 32A, i. e., only when minus current is in line l2. Thus line 10 is connected to battery (the minus pole) only when there is plus current in line I3 and minus current in line I2. The upper or operating winding of relay 6| is. connected between wire 10 and wire 51. The latter, it will be recalled, is connected to plus battery when there is plus current in line H. Thus, on the particular first impulse (plus-minus-plus) sent by the individual apparatus of Fig. 3, relay 6| is energized between wire III at minus battery potential and wire 51 at plus battery potential.

During the interval of no current in all lines, when wipers 25, 26 and 21 are between their first and second contacts, relay 6 I is. held up by the following circuit: from plus battery, through back contact of neutral line relay 31B, wire 58, wire 58', its own upper front contact, its lower or holding winding, wire 68, rectifier or one-way contact 93I, wire 68, back contact of neutral line relay 32B to minus battery. Relay 6! is materiallyslower than the line relays, especially in releasing, and is therefore unable to fall and open its own holding contact before relays 3IB and 32B close their back contacts to establish the holding circuit just traced.

Through its lower contact relay 6!, being now operated, prepares a circuit by which, if the correct second impulse for this substation follows, relay 62 is next energized. The correct second impulse of the supervisory call for substation a, sent by the apparatus of Fig. 3, it was seen, is 0, current in lines II, i2, and i3. The line relays, on this combination, connect wire 59 to plus battery and connect wire 68 to minus battery, as described. Current therefore flows from plus battery through wire 59, wire 59, lower contact of relay 6|, rectifier 932, wire 62', upper or operating winding of relay 62, wires 62" and 68' and rectifier 56I to wire 66 and minus battery. Relay 62 operates. Relay 62, once it is operated, by its own second or middle contact and wire 59", maintains a current path from wire 56 through its own upper winding during the balance of the second impulse, so that it is not deenergized when relay 6i falls back as the latter must do sometime in this impulse. By its upper contact relay 62 also closes a holding circuit, effective during the next interval of no line current, from plus battery, back contact of relay 3 IB, wires 53 and 58", upper contact and lower winding of relay 62, wires 62 and 68, rectifier 93-I, wire 66 to minus battery on the back contact of relay 3213. Like relay 6i, relay 62 is too slow in releasing to open its front contact before line relays 3 IA and 3 IB close their back contacts.

It is understood that relays 6!, 62 65 are not only somewhat slow in releasing but considerably quicker in operating than in releasing. During the second impulse just described current ceases in the holding winding of relay iii, the holding circuit previously traced being opened at the con tact of relay 3IB, but these relays being of a type and adjustment much quicker in operating than in releasing, relay 6! holds its lower contact closed until relay 62 is operated by the path described. These relays, though of quick-acting slow-release type, must not, however, be so slow in releasing as to hold up during a full current impulse in the lines. In the best adjustment they will hold up during one half thereof.

The third impulse of the supervisory call sent from the control station, as was above seen, is 0, and current in lines I I, I2 and IS. The line relays connect wire 58 to plus battery and wire 69 to minus battery during this impulse. (Wire I6, incidentally, is again connected, to wire 69 and hence to minus battery, just as on the first impulse, but since the current in line II is 0, the contacts of relay 3 IA are open and the circuit through the upper winding of relay 6! is not this time completed.) Current thus flows during this third impulse from wire 58 (plus) through rectifierS3-'-3, wire 63', winding of relay 63, wire 63", lower contact of relay 62, wire 69' to wire 69 (minus). Relay 63 operates before contact of relay 62 opens, and is held operated during the balance of the impulse after relay 52 falls via wire 69" and its own top contact, instead of via wire 63" and contact of relay 52. Its middle contact completes acircuit from plus battery through wire 96 and upper winding of relay 66 to minus battery. Relay 65 therefore operates immediately after relay 63, during the third impulse, and locks itself in operated position by the following circuit: from plus battery, through its own lower winding and its upper contact, through wire 11 and back contact of relay 33 to minus battery. At the same time relay 66 at its lower contact opens a normally closed circuit from plus battery through wire 39 and winding of vibrating relay 6!! to minus battery. However, a branch 39 of wire 39 goes to plus battery on the lower contact of relay 63, so that relay 6!) is not actually released until relay 63 releases at the end of the third impulse.

It is readily seen that when any but this particular sequence of impulses, 0 0 are received by the line relaysof substation a, either relay 6! or relay 62 or relay 63 fails to be operated. The Operation of 6| is necessary to the operation of 62, and the latter to the operation of 63 and 66. As about. to be described it is only when relay 66 is operated (and after relay 63 falls), that normally energized vibrating relay 66 is released and sends out the report impulses; Thus the substation cannot respond unless relays 6|, 62, and 63 are operated by the one correct call or sequence of three impulses. At' any other substation, e. g., b, the individual connections of relays BI, 62, and 63 between one of wires 51, 58,.and 59 (selectively made plus by the line relays) and one of wires.

61, 68, and 69 (selectively made minus), will be different, so that each substation is adapted to positive battery connection to only one of wires 51, 58-, and'59, and a negative battery connection to only one of wires 61, 68, and 69. Consequently,

only such local relays receive'full voltage as are connected between the particular two wires which are connected to the battery. But certain indirect or so called back-up circuits can be traced from positive battery to negative battery through three or more relay coils in series.

For example, at an instant when relay 64 has just operated and relay 62 has not yet fallen, certain circuits may be closed between the positive group of wires 51, 58, 59 and the negative group 6?, 68, 69, through the holdingcoil of relay 62 and the operating coils of relays 62, 63, 64 and 65. We may thus, for example, trace a backup circuit from wire 58 through the coils of relays 63 and 64 to wire 59, and thence through relay 62 to wire 68. If these three relays are operable in series by the battery potentiaL'they could improperly be energized during the interval of zero current in the lines when wires 58 and 68 are connected to positive and negative battery. No improper operation will result if the relays are so adjusted that with three in series none can be operated by the local battery voltage. However, I prefer to block the series 'circuit by one-way contact devices or rectifiers. It should be noted that the series circuit described passed from relay 64 to wire 59, or in a direction opposite to the normal course of operating current from wire 59 to relay 64. Hence the rectifier 93-4 connected as indicated will effectively block the back-up circuit but will not oppose the normal flow of operating current through the coil of relay 64. Various-other back-up circuits can be traced from one or another positive wire, when energized, to one or another of the three negative wires. But in every case such circuit involves reversal of the normal current flow through oneiof relays 62, 63, 64 or 65. The rectifiers 93l, etc., placed in the circuit as shown, block all such back-up circuits.

Phase (2).-The sending of report impulses from the substation. These impulses are controlled for time by vibrating relay and'for' character by thepositions of relay 53A and switch 54A in they fourth period and by the positions of relay 53B and switch. 543 in thefifth period.

Vibrating or pendulum relay 60 comprisesan armature 60' and a weight 60" carried on a. vibratable reed suitably connected to operate four moving contact members, sub-numberedjl" tov 4-,. shown. I -he;

having stationary contacts as natural period of the vibratable reed is suchfthat one double beat-or one complete cycle occupies substantially one full impulse period as measured from the start of onev line impulse to the next; which time it will be recalled is determined byv the speed ofshaft S in Fig. 3.

Contacts 60-2, 603 and 604 'of relay66areclosed at mid-stroke, i. e. one, quarter of an imof an impulse period after release. Contact 66lis also adjusted to be both broken andmade The actualduration of line current in any impulse. and the; deadinterval before the next impulse startsiare:

as nearly as possible at mid-stroke.

preferably about equal; The best adjustment of relays 6 l-- beingsuch as to releaseinone half of the line current duration, or in one quarter of the full impulse period, counting from the end ofi line current-in the third impulse relay 63. by its. lower contact releases. relay 60 and' the latter thereafter completes one half beat in time to operate its contacts substantially at the start of the fourth impulse period. In other words an 'im pulse to be placed on the lines as, will be seen,by--, the back contacts of; vibrating relayfifl, will be substantially in step with the arrival. ofwipers 28 and; 29 on their fourth contacts. Also, one cycle, later of relay 6.0, wipers 28. and-29' will be nearly enough-coming onto their fifth. contacts justas relay 60 againv closes its back contacts. It is in fact the function of vibrating relay 60. to maintain, for the brief time of two report impulse period-s, i. e., for two double beats, an operativesynchronism between the placing of report impulses on the lines and the contact closures of the dial switch at the control station.

As relay 60 vibrates contact 66-! alternatelyconnects the plus pole of local battery 34 to wires 19 and I8. Duringthe last half ofthe first down swing of armature 60. and'the first half of its up, swing current flows from plus battery throughv Wire 19, the left winding of relay 35, wire 11 and back contactof relay 38 to minus battery. Relay 35 operates, locking itself up from plus battery by its own nearer front contact and its right winding through wire 11 and contact of relay 38 tominus battery; The farther contact of relay 35 has now connected wire 18, through wire 18." and left. winding of relay 36-to wire 11 and minus battery;

so that in the last half of the upswing and the first half of the next downswing of armature .66

contact 60- closes. the circuit of relay 36 and.

operates the latter. Relay 36locksitself up from. i

plus battery by its nearer contact 36-'l, through.

its right winding, wire "and contact of relay,3 8 to minus battery. In like manner'relay 3 1' oper-,

ates, when armature 60 is next below mid point,-

from plusbattery, via contact 66-|, wire,19,

branch wire 'l9-',icontact 365,-left coil of relay 31, wire 11, contact of relay 38 to minus battery.

Relay 38 operates, when armature 60' is next above mid point via wires 18, 18 right hand contact of relay 31, coil of relay 38, back contact of' 38 to minus battery. The. operation of relay 38 cuts off minus, battery from wire 11 so that relays;

35 to 38 and 66 fall. Relay 38 is adjusted for rather slower release than the others lest any of the others fail to open their holding contacts before 38 itself can fall and reconnect minus battery to wire ll. Release of relay 66 restores the connection of wire 39 to plus battery and reenergizes relay 66, to remain so until again released and started vibrating by the operation of relay 66 and the fall of 63.

Contacts 60-4, 66-3, and 66-2, when closed, connect lines H, l2 and [3 respectively to wires SIT-4, Elf-3, and 6U"-2. Their first closure is in the first down and up swing of relay 60, coinciding, as pointed out above, with the fourth contact closure of the control station dial switches 28 and 29. Relay 36 is not yet operated, and these wires therefore extend through back contacts 36-2, 36-3 and 36-4 and wires 54A, 53A, and 53A" to the second wiper of report switch 54A and to the moving contacts of report relay 53A.

The second closure of contacts 65-4, 60-3 and 66-2 is in the second down and up 'swing of relay 60, coinciding with the fifth contact closure of dial switches 28 and 29. Relay 36 is operated at this time and the wires EW-A, GET-3 and 60'-2 are extended through the front contacts 36-2, 36-3 and 36-4 and wires 54B, 53B and 533" to corresponding points of report switch 543 and report relay 533.

Report switches 54A and 54B are shown (in development) as drum pole changers of type exactly like Me in Fig. 3. Any well known form of circuit changer having three conditions or positions, in each position making the and 0 connections shown, may equally well be used. In practice report switch 54A may be the drum type pole changer shown, mechanically actuated by a power track switch machine so as to show by its three positions A, B, C, the three conditions of a track switch. Report switch 54B may in practice be replaced by suitable contacts in the controller of a set of semaphore type signals, or by contacts made and broken on the relays that operate a set of trackside signal lights, these connections in either case being arranged to make the indicated and dead local battery connections for the three different semaphore or signal light conditions.

Report relays 53A and 5313 may be either the two track relays themselves or may be operated by the two track relays, whose operated or non-operated positions are to be reported. Their contacts are functionally equivalent to those of switch 530. at the control station.

In connection with track relays 53A and 53B, it is assumed that the associated track circuits are of such length that no train can enter and leave the track section in the brief interval between two successive supervisory signals at the substation, otherwise the train would pass the indicating point without causing any report to be transmitted to the control station. If conditions are such that this might otherwise occur, relays 53A and 535 should have a slow pick-up char acteristic, or other means should be provided to insure that the relays once released will not pick up before their release has been signalled to the control station.

In the fourth impulse time, report switch 54A and report relay 53A, and in the fifth impulse time, report switch 543 and report relay 533 determine which impulse of numbers '7 to 12 is sent. Tracing the conditions actually shown, when relay 6!] is released and contacts 66-4, 66-3 and 60-2 first close it is seen that line I I will be connected to the pole of the local battery 34 by wire 60-4, back contact 36-2, wire 54A, second wiper of report switch 54A, the adjacent conducting segment and the bottom wiper. At the same time line I2 will connect by contact 65-3 to wire 60-3 which leads via back contact 36-3, wire 53A, lower contact of relay 53A, and fourth wiper of report switch 54A to insulation. Line 13 will connect by contact 65-2, wire 60'-2, back contact 36-4, wire 53A", upper contact of relay 53A, fourth wiper from top of switch 54A, conducting segment adjacent, and third contact from top, to plus battery. Since substation a is shown below the control station these battery connections respectively cause downward or, per convention, minus current in line H, 0 current in line l2 and upward or current in line I3. This is impulse number 11 of the table.

Tracing the local battery connections to the three lines that may similarly be made both in the fourth and in the fifth impulses, when report switches 54A and 54B are in their A, B or C positions and when report relays 53A and 53B are either operated or not, we find that for either impulse period any one of impulses numbers 7-12 may be put in the lines.

It will be understood that the meanings assigned to these impulses, i. e., the particular combination of a track relay position with a track switch or a trackside signal position that each impulse represents, may be more or less arbitrary provided they agree with the meanings assigned to the various arrangements of lighted and unlighted lamps in indicating circuits Na" and 55a" at control station. Suitable assignments of report impulse meanings have been suggested above when describing their reception at the control station. For example in the tabular arrangement thereabove given will be found that a number 11 impulse received in the fourth period (which we have just seen is the one sent out by substation a. as the parts are shown) will light lamps 45a and 46a, and that these may have the meaning track switch is normal with track relay No. 1 energized.

Before passing to the reception of the control call the possibility of a modification making somewhat more extended use of vibrator may be pointed out. It will be noted that the vibraator 6i] and associated relays 35 to 38 constitute in effect a timer or distributor operating in approximate but workable synchronism with'the controlstation dial switches during the two impulse periods 'used to transmit report impulses from the substation. It is readily seen that the whole group of five impulses which constitutes the supervisory call with the report impulses or the control call with the controlling impulse, could be timed at the substation by a vibrator like 60 and a counting relay chain similar to relays 35 to 38, but arranged to run for four impulse periods instead of two.

In such an arrangement the vibrator would start at the end of the first, or marker impulse. Each of the call receiving relays 6| to- 64 would be dependent on a relay of the counting chain and also dependent on the combination of currents flowing in the lines; so that it could be picked up only during a particular one of the five consecutive impulses, and then only by a particular combination of line currents. If the three combinations constituting the supervisory or control call were received in the right time sequence, circuits would be set up to transmit a supervisory signal or receive a control signal as in Fig. 3.

7 until the beginning of the third impulse.

' Phase (3).The reception ofthe control call battery on wire 59 and minus on wire 69.

Parenthetically, wire 10, by relay 33, is also connected to local battery at the minus pole; but this has no local effect, not even on relay 6| to which leads, because wire 51 is dead. The plus current is in line l3 merely because the minus current in lines I I and I2 must have a return path. In other words the minus current in lines H and I2 conveys the full signaling significance 1 of this impulse, as is the property (already pointed out) of impulses numbers '1 to 12. V

With relay 62 operated and with plus on wire 59 and minus on wire 69, current flows via wire 59 through rectifier 93-4, wire 64, winding of relay 64, wire 63", lowest contact of relay 62, .wire 69' back to minus by wire 69. Relay 64 opcrates. Relay 62 shortly falls, opening this circuit at its lowest contact, .butrelay '64 holds itself operated as long'as the line impulse lasts from plus by wire 59,recti'fier '934, wire '64(, its winding and upper contact, wire 64" and wire '69 back to minus battery. 7 r V I At the end of the third impu'lseand before relay 64 falls the line relays go to the positions shown and a circuit is established from plus battery on back contact of line relay 3|B, via wire 58, rectifier 933, wire 65', lower contact of relay 64, winding of relay '65, wire 65", rectifier 93--|, wire 68, contact. of relay 323 to minus battery. Relay 65 thus operates at the end'of the third impulse. Relay 64 shortly falls but relay 65 is held operated for as long as the line relays stay as shown, 1. e., until the next or fourth I impulse begins, by the circuit from plus on contact of relay 3|B, wire 58, upper contact and winding of 65,-wire 65", 93-|, wire 68 back to minus at contact of 32B. Relay 65 is thus found operated, and its lower contact closed, when the fourth or controlling impulse begins.

7 Before describing the result of the controlling impulse about to be received it may betobserved that each of therelays 6| and62 is energized only 7 for the duration of the impulse which picked it up and the succeeding interval between impulses, and relays 63 and 64 only for the duration of the impulse. Furthermore, each relay beyond 6| is energized only if its appropriate impulse is received before the preceding relay has had time to drop. Hence, the third relay, 63 or 64, can be picked up by one and only one sequence of three successive impulses. But the same impulse combination should not be repeated in two consecutive impulses, such as the second and the third; for relay 63 or 64 would then respond to'the same combination-as relay 62; and if the relays operate very rapidly, 62-and 63 or 64 might pickjup successively during the single impulse intended for relay 62. The same limitation does not apply to relays 1| to 16, for they aredependent upon relay 65 which closes onlyafter the lastpreceding -impulse has ceased.

Phase (4).Reverting to the condition at the start of the fourth impulse, with relay 65 operated, we find that wires 51, 58 and 59 lead retional relays.

spectively-through relays 1|, 12, and 13 with attendant rectifiers 93'5, 936-and 931', through their common wire 88, lower contacts of relay 65 and wire 89, thence through one of relays 14, 15, and 16 to wires respectively 68, 61, and 69.' As

we have already seen, impulse numbers '1 to 12 13 is operated depends on the current in line H; I

which of relays '14, 15, and 16 depends on the current in line 2. Since these six controlling impulses (see table) comprise plus current in line H with either plus or 0 in line |2, 0 in line with either plus or minus in line l2, and minus in line H with either 0 or in line l2, we may have relay 1| operated with either relay or 14, we'may have relay 12 operated with either relay 15 or 16, we'may have relay 13 operated with either relay "or 16. The arrows leading from the contacts of these relays and designated A, B, C, and 'N, R, represent control wires leading to the operating elements of track side sig- For a single example, theoperation of relay 1| with" nal groups and of a track switch machine.

relay 14 will put plus battery on control wires C and R. Using the assignment of meanings sug- 'geste'd in the discussion of the controlling impulse phase of the control station circuit, this would cause the trackside signals to be set for I proceed west bound and the track, switch to be moved to reverse.

Fig. 4 shows, very diagrammatically, one modification of the substation circuit just described.

ing relay. The attainable speed of reliable operation would be increased if this restriction were removed, i. e. if the receiver were operative even with instantaneous release of the relays. can be accomplished by the use of certain addi- Fig. 4 also incidentally illustrates certain possible modifications of the line relays.

This

As in Fig. 3a, relays 3|A, 32A, and 33 are polar V relays biased to the open position and connected in lines, I2, and I3 respectively. The series neutral relays 31B and 32B of Fig. 3 are replaced by local relays, which are identified by the same reference characters, each having two coils, one

, or the other of which is energized at either energized position of the associated polar relay.

Thus, as in Fig. 3, polar relay 3|A connects wire 51 or 59 respectively to positive battery when positive or negative current flows in line I; and

connected between wires 58 and 68. It is there fore energized during the intervals between line I! and I2. This relay connects positive battery alternately to wires 9| and 92; to 9| during each impulses, i. e., when current is zero in both lines lay 86.

current impulse in the line conductors and to 92 during each interval between impulses.

The connections shown are adapted for response to the calls described for substation 01.,

R/elays 5! to 64 are connected for response to these impulse combinations as in Fig. 3; i. e., their operating circuits are connected respectively between wires 5? and 19, wires 59 and 68, wires 58 and 6S, and wires 59 and 69. But these operating circuits are dependent upon contacts of relays BI, 83, and 85, with the result (as explained hereafter) that relay 62 can close only during the second impulse of a signal and relay 83 or 65 only during the third impulse. Since each relay is restricted to operation during its proper impulse, repetition of the same impulse in succession is permissible. It will be recalled that such repetitions were barred in connection with Fig. 3a. This permits the operation on three line Wires of 216+2=108 instead of 180+2=90 substations.

Relays Bi and 8! to ill constitute a counting chain controlled by the contact reversals of' re- The first, or marker impulse operates relay 5]. As previously stated the marker impulse is chosen from a group of combinations reserved exclusively for markers; hence relay 5i can operate only on the first impulse of a call. When closed it holds up over a circuit from positive battery through its lower coil and first contact to negative battery at the second contact of relay 8?. At the same time its second contact completes a path from wire 92 through the upper, or operating coil of relay 81 to negative battery at relay 8?. So long as the first impulse continues relay at is deenergized and wire 92 is dead; but when the'line impulse ceases relay operates, energizing wire 92 from positive battery. Relay 8i now operates and holds up over the obvious circuit through its lower coil and first contact. In like manner each relay of the chain in closing establishes the operating circuit for the next relay at its right. The latter relay closes at the next reversal of relay 86. Thus relays BI and Si respectively operate at the start and finish of the first impulse; 82 and 83 at the start and finish of the second impulse; 8t and $5 at the start and finish oi the third impulse; and 86 and til at the start and finish of the next impulse that is sent from the control station. During the normal program of supervisory calls and reports this will be the initial impulse of the succeeding substation call; for the substation line relays are not designed to respond to the relatively weak currents which constitute the report impulses sent from the substation. If the call received is a control call instead of a supervisory call, the next impulse sent from the control station is a control impulse in the fourth period, towhich relays 86 and 87 will respond. In either case relay Bl will operate before any impulse received over the lines can cause a false response.

When relay 87 operates it breaks the negative battery connection for the holding circuits of all previous relays, which thereupon release. In order to avoid possible vibrator action at relay 81 its operating circuit is transferred to negative battery over its first contact, and the relay remains closed until the next reversal of relay 80, when it drops, completing the restoration of the counting chain to normal position.

At the end of the first line impulse thethird contact of relay 8i completes the operating circuit for relay t2. If operated by the appropriate second impulse, the latter relay holds up over an obvious circuit through its first contact and lower coil until the holding circuit is broken as already described at relay 8i. At the end of the second impulse the operating circuit is broken at the fourth contact of relay 83. Hence relay 52 can operate only during the second impulse.

Provided relay 62 has operated as described during the second impulse, operation of relay 83 will complete the following circuit: From wire 69 through second contact of relay 62, third contact of relay 33 and back contact of relay $5 to the top of operating coils of relays 63 and 6d; thence through the former and a rectifier 93 towire 58 and through the latter and another rectifier to wire 59. If the third impulse is that of the supervisory call, wires 58 and 9 will be connected to battery and relay 63 will energize. the third impulse received is that of the control call, wires 59 and 59 will be connected to battery and relay 64 will operate. In the former case wires 39 and 519 are connected to positive battery for the duration of the impulse only. This resuits in transmission of report impulses as described in connection with Fig. 3a. In the latter case relay holds up over its lower coil until the end of the fourth impulse (when the holding circuit is interrupted at relay 8?). of the third impulse the fourth contact of relay establishes a connection from wire 88 through the second contact of relay 64 to wire 89. Relays li'to it (see Fig. 3a) are thereby prepared to receive a control impulse in the fourth period.

The operating circuit for relays 63 and 64 is broken by relay 85 at the end of the third impulse. Hence these relays cannot be improperly operated by the fourth impulse instead of the third. As in Fig. 3a. the rectifiers 93 block series circuits which would otherwise exist other than the proper operating circuits from positive to negative battery, e. g., from positive battery through the left hand coil of relay 32B, wires 69 and it, coil of relay ti, wire 5? and right hand coil of relay MB to negative battery.

One embodiment of this invention has been shown diagrammatically in Fig. l and completely in Figs. 3 and 3a. Certain modifications have been shown in Figs. 2 and 4, and other modifications have been described in the specification. Many other modifications which fall within the scope of the invention as defined by the following claims will occur to those skilled in the art.

What I claim is:

1. In a remote control system, three lines, means including a source of current for impressing current of different characteristics simultaneously on each line and means for selecting the impressed current characteristics in accordance with a code involving successive impulses and a combination of current characteristics on each line in each impulse.

2. In a remote control system, more than two stations all connected by three conductors, a source of current, a transmitter at a first station sending a call signal, for one of the other stations, composed of distinctive current combinations on the three conductors in successive impulses, a receiver at the called station responsive to the call At the end trol station and substations connected by three conductors including means at the control sta tion'for transmitting either of two calling codes to each substation, means responsive at a sub-- from said first station.

signal, an operating unit at the called station,

and a transmitter at the called station responsive to said receiver and to said operating unit for transmitting to said first stationa report signal, which'report signal involves distinctive current combinations in' one impulse, to indicate the condition of said operating unit.

: 3. In a remote control system, a plurality of Stations, three conductors interconnecting said stations, a transmitter at a first station sending a 'call of successive currentimpulses on combinations of said three conductors, including combinations when no current is sent on certain conductors of each combination, the first'impulse of the call being one of several reserved'for first impulses of calls, and a receiver at one of the.

rent combinations and the second class selected from a difierent set of current combinations, and receivers responsive to signals initiated by'an impulse group of the first class but not responsive to any overlapping group of impulses.

5. A remote control system comprising'stations connected by three conductors and signalling devices including a source of current in the stations adapted to communicate one with another in a code characterized by a sequence of impulses and by the presence or absence and polarity of ourrentin certain conductors during each impulse.

6'. A remote control systemV'comprising'aconstation to the first code to transmit two supervisory'signals, and means. responsive at a substation to thesecond code to receive a control signal indicating a combination of; two desired operations.

'7. In a remote control system, two stations con-v l nected by three conductors only, at least two opcrating units at one of said stations, and means for transmitting over the conductorsin a single impulse a control signal indicating the :desired one of three possible operations for one operating unit and the desired one of two possible operations for a second unit.

8. In airemote control system, two stations con? nected by three conductors only, groups of operating units,.and means for transmittingover the conductors in a single impulse a report signal indicating one of three conditions in one operating unit or group and one of two conditions in a second unit. r

9. In a remote control system, a control station and substations, operating units at said substations, means including threeline conductors for communicating messages between the control station and -a substation in'a code fcomposed of.-

successive impulses on characteristic-combina;

tions of said'conductors, each message including a substation call in twoimpulses' to identify a desired substationand a signal in'a subsequent impulse to indicate the condition of an operating unit at the called substation.

10. A train dispatching system comprising a control station, and substations connected by 'lines, and a receiver at the other station responsive to the combination of potentials on the lines,

three line conductors, a transmitter at the con- 'trol station automatically sending out a recurat the control station for suspending the receipt 1 of a supervisory signal by manual intervention and substituting a control signal to the same substation. a 7

11.'In a train dispatchingsystem, a controlstation and substations communicating cover three 'line wires, operating units at the substations, automatic means for signalling between the control station and each substation in turn in a recurrent program to transmit information concerning operating units at the substations, and manual means for suspending the automatic program for the transmission of signals to specific substations V V r 12. In a train dispatching system comprising a control station and substations: communicating over three line wires, operating units at the substations, indicators at the control station indicating continuously the condition of operating units at substation, and recurrent means for correcting the indications of twoindicators at one and the same time and for correcting the indications of all indicators at intervals so short, as to' be substantially equivalent for practical purposes to continuous supervision.

13. A train dispatching system comprising three lines, stations distributed along the lines, a source of current, and a transmitter for impressing voltage upon' the lines at each station,

14. A train dispatching system 7 comprising three lines, stations distributed along the lines, a source ,of current and a transmitter for impressing voltage upon the lines at each station,

and a receiverfat each station including electron ic relays responsiveto'potential differences between the lines.

15. A train dispatching system comprising two stations connected by three lines, a source of energy and a transmitter at one station to establish a combination of potentials on the said receiver including one electronic relay having a filament and grid connected respectively to the first and. second lines and another .electronic relay having a filament and grid connected respectively to the second and first lines,

the two relays producing three distinctive responses according as the firstline orthe sec- 0nd line or neither is at a higher potential than current source and a switch at the control station automatically establishing successive current combinations in the lines to call the substations, a second switch to modify one of the current combinations when a unit at a substation is to be operated,'and a. third switch co-operating with the first and second switches to select the current combination impressed upon the lines'in transmitter and two' receivers connected by 71';

three lines, automatic means in the transmitter for sending a program of successive current combinations over the wires calling each receiver selectively in turn to cause a responsive signal therefrom, manual means to modify the calling combinations for one receiver and thereby to control an operation at the receiver, andautomatic means to restore the normal program of current combinations after the modified combinations have been transmitted.

18. In a train dispatching system, three conductors, substations associated therewith and a transmitter comprising a source of current, switches and a distributor whereby groupsoi impulses constituting call or control signals for successive substations are transmitted over the conductors in a recurrent program, the current combination transmitted being invariable in certain impulses, variable in other impulses for selection as between supervisory or operative response at the substations and variable'in other impulses to select particular operations desired at the substations.

19. In a train dispatching system, a control station and substations connected by three lines, selectors at the control station for each substation, a-distributor at the control station connecting the lines successively to certain points corresponding to successive impulses of a signal to a substation and a second distributor connecting the points successively to difierent ones of said selectors corresponding with different substations, the signal transmitted to each substation depending upon certain permanent connections to the second distributor and upon manual operation of the particular selector. 7

20. In a train dispatching system,,threelines connecting a control station to substations, a signal selector for each substation at the control station, a switch at the control station transferring line connections successively to different signal selectors and a second switch establishing connections for successive impulses during connection to one selector.

21. In a train dispatching system, a control station and substations connected by three line wires, signalling units at the control station, one for communication with each substation, and concatenated distributing switches at the control station for associating the signalling units successively with the line wires and for establishing successiveimpulse periods for each unit.

22. In a train dispatching system comprising a control station and substations connected by three line wires, a source of current, transmitters at the substations for variably applying current from said source to said line wires, a receiver at the control station adapted to give three indications of conditions at the substation selectively according as the current in a first line wire is positive, negative or zero, and a second receiver at the control station responsive jointly to current in the first line wire and in a second line wire to give additional indications.

23. In a train dispatching system comprising a control station and substations connected by three line wires, receivers at the control station, one for each substation for reception of supervisory signals, and concatenated distributing switches for associating the receivers successively with the line wires and for establishing successive impulse periods during the association of each receiver, successive control and report impulse periods being established during each such association.

24; In'ja train dispatching system comprising a control station and substations connected by three line wires, a receiver at the control station responsive, to current combinations in the line wires adapted to respond selectively during a single. line impulse to one of three positions of one selector ata substation and to one of two positions of a second selector at a substation.

25. In a train dispatching system, a control station connected by three line wires to a substation, aplurality of units at the substation, and a sender at the substation adapted to transmit during a single line impulse a supervisory signal indicating one of two conditions of one unit and one-of three conditions of another unit.

26. In a train dispatching system comprising a control station and a substation connected by three line wires, a receiver at the control station and a receiver at the substation, means at the control stationfor controlling the receiver at the substation, and a sender located at and responsive to-thereceiver at the substation for transmitting signal impulses isochronously with said receiver at the control station.

27. In a train dispatching system the sender at the receiving station as described in claim 26 comprising a vibrating relay.

28. In a'train dispatching system, stations connected by three line conductors, a source of current, means at each station for variably applying current from said source to the line conductors, a receiver at one station comprising two polar relays responsive to current in one line conductor,

the first adjusted to close one contact when the current is positive and another when the current iszero or negative, the second adjusted to close one contact when the current is negative and another when the current is zero or positive, trafiic controlling devices ,at said stations, and three circuits for variably controlling said devices, one of said circuits being selected jointly by the two relays in response to positive, negative, and zero current in the line.

29. In a train dispatching system, stations connected by three line wires, a source of current, means at each station for variably applying current from said source tosaid line wires, a receiver at one station comprising a polar and a neutral relay, the polar relay actuated by current in one line wire to close one or another circuit when the line current is positive or negative and neither relay actuated when the current is zero, the neutral relay, actuated by local energy through the contacts of the polar relay, being released to close a third circuit when the line current is zero, and trafiic controlling devices at said stations variably operated upon the closing and opening of said circuits.

30. In a train dispatching system, stations connected by three line Wires, a source of current, means at said stations for variably applying current from said source to said line wires, a pair of local wires at one station, means at said one station for energizing one or the other of said local wires in accordance with current in one line wire, a second pair of local wires, means at said one station for energizing one or the other of said second pair of local wires in accordance with current in another line wire, and a receiving element at said one station responsive only to one combination of energized wires in the first and second pairs.

31. In a'train dispatching system, a receiver comprising a battery and a group of wires, a transmitter for sending signals to said receiver, 

